We have developed a new theory of renaturation kinetics, which differs from the existing theory in two ways: (1) the rate of zipping of base pairs is included in the theory, and (2) the fact that renaturing single strands are only 2/3 complementary on the average is taken into account in a different way. This theory explains well the deviations from linearity in reciprocal-second-order plots seen in renaturation experiments followed by optical density or S1 nuclease. While we have performed several experiments, verifying the theory, we wish to perform more experiments to further verify the theory and to re- examine the effect of single strand length on the kinetics.